Arrangement for measuring duty cycle



July 26, 1949. T Q HANA 2,477,370

ARRANGEMENT FOR MEASURING DUTY CYCLE Filed Nov. 22, 1946 o AMPLIFYINGO Ampl Hude 'u- FIGA 52 eo 6'; l INVENTOR. -0 66 THOMAS c. HANA 63 AMPLIHER BY y #o o ATToRNE Patented July 26, 1949 *f UNITED STATES PATENT OFFICE ARRANGEMENT FOR MEASURING DUTY CYCLE v Thomas C. Hana, Great Neck, N. Y., assignor to Hazeltine Research, Inc., Chicago, Ill.,a corporation of Illinois Application November z2, i946, serial No. 711,111

11 claims. 1

lrepetition time, duty cycle may also be expressed as the product ofthe pulse width and the pulserepetition frequency.

Power is ordinarily measured as an averag value over a relatively long period of time, although the useful power of a pulse-modulated wave-signal translating system such as a transmitter, termed the peak power thereof, is contained in the radiated pulses of radio-frequency energy. Since a pulse transmitter produces a pulse-modulated signal for an interval of time which is short with respect to the period of a single operating cycle, the average power developed by the transmitter is usually low in comparison with the peak power. The ratio of the average power to the peak power of such a transmitter also comprises the duty cycle of thetransmitter.

In many pulse-modulated wave-Signal translating systems such as transponder beacons, the peak power is. usually fairly constant while the durations and the repetition frequencies of the transmitted pulse-modulated wave signals vary depending upon operating conditions. Such variations alter the average power produced by the system and also the duty cycle thereof. While it may be desirable in a pulse-modulated transmitter to utilize high peak powers to obtain strong signals and a large resulting range, it is also advantageous from an operating standpoint to mainf tain a low average power in spite of varying repetition rates and pulse durations to avoid overloadl ing tubes and circuit components, thus prolongan arrangement for measuring the duty cycle of recurring pulses having closely spaced leading and' trailing edges.

It is a further object of the invention to provide a sensitive arrangement for measuring the duty cycle of recurring pulses having leading and trailing edge portions, which arrangement permits the use of a relatively insensitive meter in the circuit thereof.

It is an additional object of the invention to provide an arrangement for measuring the duty cycle of recurring pulses having leading Yand trailing edge portions and relatively long pulse durations.

In accordance with the invention, an arrangefment for measuring the duty cycle of recurring pulses having leading and trailing edge portions 'comprises a pulse generator responsive both to the leading and the trailing edge portions for deriving therefrom related pulses having substantially constant amplitudes and effectively the same durations and repetition rates as the corresponding recurring pulses. The arrangement also yincludes a meter responsive to the related pulses for developing an indication which is directly proportional to the durations and the repetition rates of the related pulses to indicate the duty cycle of the recurring pulses.

vFor a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring now to the drawing, Fig. 1 is a schematic diagram of a complete arrangement in accordance with the invention for measuring the duty cycle of recurring pulses; Fig. 2 is a series of graphs representing various wave forms which are utilizedin explaining the operation of the arrangement of Fig. 1; Fig. 3 is a schematic diagram, of a portion of a modified form of the invention; and Fig. 4 represents schematically an additional modification of the tion. y y

Referring now moreparticularly to Fig. 1 of the drawing, the arrangement f'or measuring the present invenduty cycle of recurring pulses having leading andl ventional differentiating circuit Il havingwa pair of input terminals I2, I2 and an output circuit which is connected to the input circuit of eachv of two :amplifying and clipping units I3 and I4. The amplifying and clipping unit I3 includes well-known circuits for amplifying pulses of a given polarity and for clipping pulses of the opposite polarity to obtain control or triggering pulses at the initiations of the recurring pulses. Unit I4 is similar to unit i3 and includes conventional circuits for amplifying pulses of the aforesaid opposite polarity and for clipping pulses of the previously mentioned given polarity in order to obtain triggering pulses at the terminations of the recurring pulses.

The arrangement for measuring duty cycle also comprises a means or unit I5 responsive to the control pulses, and hence to the recurring pulses, for deriving therefrom related pulses having sub-v stantially constant amplitudes and effectively the same durations and repetition rates as the corresponding recurrent pulses. This means includes a pair of gaseous discharge means, specifically thyratrons I6 and I1, the input circuits of which are connected, respectively, to the output circuits of units I3 and I4. The control electrode of thyratron i6 is connected to ground through a grid-leak resistor I8 and to the ungrounded output terminal or" unit I3 through a coupling condenser I9 and an input terminal 29. Similarly the control electrode of thyratron I1 is connected to ground through a grid-leak resistor 2| and to the ungrounded terminal of unit I4 through a coupling condenser 22 and an input terminal 23. The anode of thyratron I6 is connected directly to the anode of thyratron I1 and is, in turn, connected to a source of potential +B through a resistor 25 which has a relatively high value. Unit i5 also includes an energy-storage means in the form of a transmission-line section 21 which may comprise series-connected inductors 28, 28 and shunt-connected condensers 29, 29. The high-potential terminal of the transmission-line section 21 is connected to the anodes of thyratrons i6 and AIl while the other'terminal is grounded. Transmission-line section 21 has a round-trip time-delay characteristic which is greater than the duration of any of the recurring pulses which may be applied to the input terminals I2, I2 of the diiierentiating circuit II.

A pair of discharge paths is included for the transmission-line section 2l. One of these paths which, under conditions to be explained hereinafter, is effective partially to discharge the transmission-line section 21 includes the anodecathode path of the thyratron IB and a seriesconnected combination in the cathode circuit of the thyratron comprising a relatively insensitive `direct-current meter 30, a resistor 3|, and a source of potential +B1.

The meter 30 is onewhich is adapted to measure average values and is -calibrated to indicate duty cycle directly. The potential of the source +Bi has a lower value than that of the source +B and is poled to main- -tain the thyratron I6 normally in a nonconducty4 f i l ence to the graphs of Fig. 2, it will be assumed initially that the transmission-line section 21 is charged to the potential of the source +B and that the thyratrons I6 and I1 are in a nonccnductive state. A signal comprising recurring rectangular pulses of the type illustrated in curve A of Fig. 2, the duty cycle of which is to be measured, is applied to the input terminals I2, i2 of' the.differentiating circuit II. Since the differentiating circuit II is responsive to the leading and the trailing edge portions of the recurring pulses, these pulses are differentiated therein to produce short duration, alternately positive and negative pulses at the output terminals thereof, as illustrated -in curve B. Unit i3 amplies the positive output pulses from the differentiating circuit Il and clipsthe negative pulses so that a signal havingathe wave form illustrated in curve C of Fig. 2 results at the output terminals of unit I3. Unit I4 is effectively responsive only to the negative pulses derived by the differentiating circuit I I from the trailing edges of the recurring pulses since the positive output pulses from cir--v cuit I I are clipped by unit I4. The derived negative pulses are amplified and reversed in polarity by the unit I4 to produce a signal which has the Wave form illustrated in curve D.

At time to the positive pulse of curve C is applied to the input circuit of the thyratron I6 and, since it exceeds the critical value of control-electrode cathode voltage or striking potential, it causes ionization to take place in the tube. The transmission-line section 21 commences t0 discharge at a constant rate through the anodecathode path of thyratron I6; the meter 30, the cathode resistor 3i, and the source +B1. At the time t1 the positive pulse of curve D is applied by unit I4 to the control electrode of thyratron I1 and the gas therein also becomes ionized so that the thyratron I1 is rendered conductive. As a result, a low-impedance path between the anode of thyratron I6 and the sourcev +`B2 is provided. Because of this low-impedance path and also because the source +B2 is at a materially lower potential level than the source +Bi in the cathode circuit ofthe rst thyratron I6, the anode of thyratron I6 falls to a potential which is lower than that of its cathode. Consequently, the dow of space current through the thyratron I6 and the meter 3U abruptly ceases.

The completion of the discharge of the transmission-line section 21 is then effected through the anode-cathode path of tube I1. After deionization is complete in the thyratron I1, the transmission-line section 21 is charged from the source +B to its initial value through the resistor 25 at a rate determined by the value of the resistor 25 and the effective capacitance of the condensers 29, 29. Unit I5 is then at its original condition and, when actuated at times t2 and ta by additional control pulses of the type illustrated in curves C and D of Fig. 2, repeatsthe abovedescribed cycle of operation.

As a result of the action of the wave-shaping arrangement I u and the conductance variations effected in the thyratron I6, rectangular pulses having steep leading and trailing edges, as illustrated in curve E of Fig. 2, are translated by the thyratron I 6L and the meter 30. Since these pulses are derived from the recurring pulses of curve A, the pulses applied to the meter 30 are related to the recurring pulses of curve A. The uniform discharge characteristic of transmission-line section 21 results in the translation of pulses having substantially constant amplitudes by the meter the ungrounded output terminal of unit 3|. In view of the fact that the edge portions of the pulses of curve E effectively correspond in time with the corresponding leading and trailing edges of the recurring pulses of curve A, the durations of the current pulses which are applied to `the meter 30 are directly proportional to the durations of the recurring pulses.` Additionally, the pulses which are applied to the meter 30 are directly proportional to the repetition frequency of the recurring pulses since a pulse is translated by the meter for'every recurring pulse which is applied to terminals I2, I2 of the differentiating circuit II. Since the amplitudes of the related pulses are substantially constant, the meter 30, which measures the average value of the related pulses over individual periods thereof, indicatesV the product of pulse duration and pulse-repetition frequency and, hence, the duty cycle of the re curring pulses.

In view of the fact that related pulses of relatively large energy content are translated by the thyratron I6 and applied to the meter 30, a relatively insensitive meter is eiective to provide an accurate indication of the duty cycle of the recurring pulses applied to the arrangement. The described arrangement is particularly well adapted to respond to pulses having steep leading and trailing edges and is also capable of measuring the duty cycle of pulses of extremely short durations. It will be evident that the frequency of the recurring pulses which may be measured by the above-described arrangement is determined by the deionization time of the thyratrons, particularly the second thyratron I1 and the time constant of the charging circuit of the transmission-line section 21. It will also be manifest that the round-trip delay characteristic of the transmission-line section 21 effectively determines the duration of the longest recurring pulse which may be translated by the described dutycycle measuring arrangement.

A portion of a modiiied arrangement in accordance with the instant invention which is capable of measuringthe duty cycleof recurring pulses of longer durations or of pulses of shorter repetition rates than the Fig. 1 embodiment is illustrated schematically in Fig. 3 of the drawing. The arrangement there represented comprises a multivibrator including a pair of pentode tubes 44 and 45. The input circuit of the pentode 44 is adapted to be connected to the ungrounded output terminal of the amplifying and clipping unit I3 through a coupling condenser 46 and an input terminal 40. The input circuit of -the pentode 45, which includes a grid-leak resistor 41 in shunt therewith, is adapted to be' connected to I4 through a ccuplingcondenser 48 and an input terminal 43. A source of potential +B is connected to the anode of the pentode 45 through I the series combination of a meter 49 and a resistor 50. This source is also connected to the screen electrode of pentode 45 through a voltagedropping resistor 5I and to the anode, screen elec- Ipentode 45. The screen electrode of the pentode A145 is connected to ground through a condenser 'more positive.

51 and the suppressor electrode thereof is connected to a source of negative potential --Bl through a resistor 59.

Considering now the operation of the Fig. 3 modification, it will be assumed initially thatthe pentode 44 is conducting while the pentode 45 is in a nonconducting state. It will be further assumed that control or triggering pulses similar to those illustrated in curves C and D of Fig. 2, but of opposite ornegative polarity, are adapted to be applied to the input terminals 40 and 43 from a wave-shaping Iarrangement similar to the wave-shaping arrangement II) of the Fig. l embodiment. The application of a negative control signal at time tu, as illustrated in curve F of Fig. 2, to the control electrode of the pentode 44 reduces the flow of space current therein thereby causing the screen electrode to become This translates a more positive voltage` through the coupling condenser 56 to the suppressor electrode of the pentode 45, thus initiating the flow of spa-ce current therein. As a result the anode of the pentode 45 becomes more negative and a negative signal is applied to the control electrode of the pentode 44 through the condenser 55 thereby driving the pentode further toward cutoff. This process is cumulative and the tube 44 is driven rapidly to cutoff at time to while the tube 45 becomes conductive. At time t1 a negative control pulse, as illustrated in curve G of Fig. 2, is applied to the control electrode of the pentode 45, thus reducing the flow of current therethrough. Consequently the anode potential approaches that of the source +B so that a positive voltage is translated through the coupling condenser 55 to the control electrode of the pentode 44. As a result tubel 44 becomes conductive so that the'potential on the screen electrode thereof decreases and a negative voltage is translated to the suppressor electrode of the pentode 45 through the coupling condenser 56. Pentode 45 thereupon becomes less conductive and the above-described action becomes cumulative whereupon tube 45 is driven abruptly to cutoff. At time t2 a second negative control pulse is applied to the input circuit of the pentode 44 followed by the application of a similar pulse at time ta to the control electrode of the pentode 45, and the above-described cycle of operation is repeated. During the intervals in which the pentode 45 is conductive, the meter 49 is actuated by pulses of substantially constant amplitudes similar to those of curve E oi Fig. 2 and, as has been previously explained in connection with the Fig. lembodiment of the invention, proyides an indication representing the Yduty cycle of the recurring pulses'which are applied to the input terminals of the arrangement.

From the above description and explanation of the operation of the Fig. 3 embodiment of the invention, it will be apparent that the multivibrator including the pentodes 44 and 45 comprises the means having two operating conditions which is responsive to triggering pulses which are applied to the input terminals 40 and 43 and is caused thereby to alternate between one operating condition and the other to derive related pulses having substantially constant amplitudes and effectively the same durations and repetition rates as the corresponding recurringI pulses. It will also be manifest thatthe meter43`comprises ameans for `utilizing the related pulses for providing an indication which is directly proportional to the durations and the repetition rates of -nected to a meter 61 through resistors 62 and 66.

The series combination of a diode 64 and a biasing source 55, the positive electrode of the lat-l ter being connected to the cathode of the diode,

is connected in shunt with the series-connected resistor 66 and the meter 61.

In considering the operation of the last-described arrangement, it will be assumed that recurring pulses similar to those illustrated in curve A of Fig. 2l are applied to the input terminais 6!! and 63. The recurring pulses are amplifled in unit 6l and are applied to the meter 61 through the voltage-dropping resistor y62 and the resistor 66. Recurring pulses which exceed a predetermined amplitude are effective to overcome the bias afforded by the source 65 so that the diode 6i becomes conductive. the potentials whichv exceed this predetermined value appear across the voltage-dropping resistor 62 so that only a signal which is limited to the desired amplitude is applied to the meter 61. Indications afforded by the meter 61 will indicate the duty cycle of the recurring pulses which are applied to the input terminals 66 and 63 of the arrangement.

While several forms of the present invention have been described, for particular applications one embodiment may possess certain desirable advantages over the others. As has been previously mentioned, the arrangement of Fig. 1, which utilizes thyratrons in the circuit thereof, permits the use of a relatively insensitive meter without sacrificing accuracy, thus enabling the over-all cost of the arrangement to be reduced. The multivibrator arrangement of Fig. 3 which, unlike the arrangement of Fig. 1 which utilizes thyratrons, permits the use of two tubes in a single envelope, thus reducingr space requirements and simplifying connection problems. The multivibrator arrangement of Fig. 3 also is adapted to accommodate longer pulses or recurring pulses having greater repetition rates. Additionally the last-mentioned type of arrangement permits the use of vacuum tubes, which are characterized 'by longer life, rather than gas-iilled tubes. For some applications the relatively simple arrangement of Fig. 4 is entirely satisfactory.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes Consequently,

8 thereof for developing an indication which is directly proportional to the durations and the repetition ratesr'vof said related pulses to indicate said duty cycle of said recurring pulses.

2. An `'arrangement for measuring the duty cycle of recurring pulses having leading and trail@ ing edge portions comprising, a pulse generator responsive both to `said leading and trailing edge portions of said recurring pulses for deriving therefrom related pulses having substantially constant amplitudes and effectively the same durationsand repetition rates as the corresponding recurring pulses, and a meter responsive to said related pulses for developing an indication which is directly proportional to the durations and the repetition rates of said related pulses to indicate said duty cycle of said recurring pulses. 3. .An arrangement for measuring the duty cycle of recurring pulses having leading and trailing edge portions comprising, means for obtaining control pulses from both said leading and trailing edge portions of said recurring pulses,

and modifications as fall within the true spirit riving therefrom related pulses having substantially constant amplitudes and eifectively the same durations and repetition rates as the' corresponding recurring pulses, and a meter responsive to said related pulses for developing an indication which is directly proportional to the durations and the repetition rates of said related pulses to indicate said duty cycle of said recurring pulses.

4. An arrangement for measuring the duty A cycle of recurring pulses having leading and trailing edge portions comprising, means for differentiating said recurring pulses to obtain triggering pulses from both said leading and trailing edge portions of said recurring pulses, -means having two operating conditions responsive to saidtrlggering pulses and caused thereby to alternate between one operating vcondition and the other to derive related pulses having substantially constant amplitudes and effectively the same durations and repetition rates as the corresponding recurring pulses, and a meter for utilizing said related pulses to provide an indication which is directly proportional to the durations and the repetition rates of said related pulses to indicate said duty cycle of said recurring pulses.

5. An arrangement for measuring the duty cycle of recurring pulses having leading and trailing edge portions comprising, means for differentiating said recurring pulses to obtain triggering pulses from bc-th said leading and trailing edge portions of said recurring pulses, means including a pair of electron tubes responsive to said triggering pulses for deriving therefrom related pulses having substantially constant amplitudes and effectively the same durations and repetition rates as the corresponding recurring pulses, and a meter responsive to said related pulses for developing an indication which is directiy proportional to the durations and the repetition rates of said related pulses to indicate said duty cycle of said. recurring pulses.

6. An arrangement for measuring the duty cycle of recurring pulses having leading and trailing edge portions comprising, gaseous discharge means responsive both to said leading and trailing edge portions of said recurring pulses for deriving therefrom related pulses having substantially constant amplitudes and effectively the same durations and repetition rates as the corresponding recurring pulses, and a. meter responsive to said related pulses for developing an lndurations and the repetition rates of said related r pulses to indicate said duty cycle of said recurring pulses.

7. An arrangement for measuring the duty cycle of recurring pulses having leading and trailing edge portions comprising, gaseous discharge means responsive both to said leading and trailing edge portions of said recurring pulses for deriving therefrom related pulses ofrelatively large energy content havingsubstantially constant amplitudes and effectively the same durations and repetition rates as the corresponding recurring pulses, and a relatively insensitive direct-current meter responsive to said related pulses for developing an indication which is directly proportional to the durations and the repetition rates of said related pulses to indicate said duty cycle of said recurring pulses.

8. An arrangement for measuring the duty cycle of recurring pulses having leading and trailing edge portions comprising, a pulse generator including a pair of gaseous discharge means responsive both to said leading and trailing edge portions of said recurring pulses for deriving therefrom related pulses having substantially constant amplitudes and eiectively the same durations and repetition rates as the corresponding recurring pulses, and a meter responsive to a conductance variation of each of said gaseous discharge means for utilizing said related pulses to develop an indication which is directly proportional to the vdurations and the repetition rates of said related pulses to indicate said duty cycle of said recurring pulses.

9. An arrangement for measuring the duty cycle of recurring pulses having leading and trailing edge portions comprising, energy-storage means, a pair of discharge paths therefor, switching means responsive both to said leading and trailing edge portions of said recurring pulses for partially discharging said energy-storage means through one of said paths and for subsequently completing the discharge of said energy-storage means through the other of said paths to derive related pulses having substantially constant amplitudes and electively the same durations and repetition rates as `the corresponding recurring pulses, and a meter responsive to said related pulses for developing an indication which is directly proportional to the durations and the repetition rates of said related pulses to indicate.

said duty cycle of said recurring pulses.

Y 10 cycle of recurring pulses having leading-and trailing edge portions comprising, a transmissionline section having a time-delay characteristic greater than the duration of any of said recurring pulses, a pair of discharge paths therefor, switching means responsive both to said leading and trailing edge portions of said recurring pulses for partially discharging said transmission-line section through one of said paths and for subsequently completing the discharge of said transmission-line section through the other of said paths to derive related pulses having substantially constant amplitudes and effectively the same durations and repetition rates as the the corresponding recurring pulses, and a meter responsive to said related pulses for developing an indication which is directly proportional to the durations and the repetition rates of said related pulses to indicate said duty cycle of said recurring pulses.

11. An arrangement for measuring the duty cycle of recurring pulseshaving leading and trail l 10. An arrangement for measuring the duty ing edge portions comprising, a transmissionline section, a pair of discharge paths therefor including gaseous discharge means responsive both to said leading and trailing edge portions of said recurring pulses for partially discharging said transmission-line section through one of said paths and for subsequently completing the discharge of said transmission-line section through the other of said paths to derive related pulses having substantially constant amplitudes and electively the same durations and repetition rates as the corresponding recurring pulses, anda meter in said path for partially discharging said transmission-line section responsiveto said related plilses for developing an indication which is directly proportional to the durations and the repetition ratesof said related pulses to indicate said duty cycle of said recurring pulses.

THOMAS C. HANA.

- VREFERENCES errno 'I'he following references are of record in the 'me of this patent:

UNITED STATES PATENTS 

